Two hundred thousand Americans are alive today who suffer from the chronic effects of spinal cord injury. Traumatic brain injury is the source of 500,000 hospitalizations every year in the United States, and each year 80,000 of these patients will retain a lifelong disability.
There are two general types of spinal cord injury: complete and incomplete lesions. Complete lesions leave the patient with no motor, sensory, or autonomic function below the level of the lesion. Transection of the spinal cord is the most obvious cause of a complete lesion. The level of the injury in the spinal cord determines exactly what function will be lost, as the spinal nerves which exit the cord below this are absolutely unable to transmit signals to or from the brain. Incomplete lesions can take a variety of forms, and depending on the nature of the trauma, a range of motor and sensory abilities may be present.
Additionally, non-traumatic pathologies such as stroke and Parkinson's disease are also often characterized by a patient's inability to successfully translate a desire to perform an action into the appropriate motions of the relevant limbs. In summary, central nervous system pathologies are often responsible for varying levels of paralysis which cause immense suffering in the affected population.
Rehabilitation efforts for these patients usually focus on teaching means for using still-functioning limbs to carry out desired tasks, while trying, when possible, to recover some function in the affected limbs. In addition, a range of technologically advanced, expensive, and—unfortunately—not very satisfactory devices have been built and tested on patients. Amongst these are muscle-stimulation devices, which include electrodes that are mounted on a patient's muscles in a paralyzed limb. In response to a command, the electrodes drive current into the muscles, causing the contraction thereof. The resultant motion of the limb is typically rough, and the unnatural stimulation protocols often leave the patient's muscles tired, even after performing only a small number of tasks.
U.S. Pat. Nos. 5,178,161 and 5,314,495 to Kovacs, and U.S. Pat. No. 4,632,116 to Rosen, which are incorporated herein by reference, describe the use of microelectrodes to interface between control electronics and human nerves.
U.S. Pat. No. 4,649,936 to Ungar et al., which is incorporated herein by reference, describes an electrode cuff for placement around a nerve trunk, for generation of unidirectional propagating action potentials.
U.S. Pat. No. 4,019,518 to Maurer et al., which is incorporated herein by reference, describes methods for using an electrical stimulation system to selectively stimulate portions of the body.
U.S. Pat. Nos. 5,776,171 to Peckham et al., 5,954,758 to Peckham et al., and 6,026,328 to Peckham et al., which are incorporated herein by reference, describe methods and devices for stimulating muscles of limbs of the body, so as to achieve motion and control of the limbs in patients with central nervous system disabilities. Limb motions in each limb are commanded by external means and communicated via radio waves to apparatus implanted in the limb. Actual motion of the limb is monitored and compared to the commanded motion with the goal of attaining real-time control of the limb.
U.S. Pat. No. 5,748,845 to Labun et al., which is incorporated herein by reference, describes a device for controlling limbs of patients with central nervous system disabilities. The activity of a healthy muscle is sensed, analyzed, and used to determine input parameters to a control system of the device. Both external mechanical apparatus and direct electrical stimulation of muscle tissue are described as means for inducing movement of the disabled limb.
Many patents disclose other methods and devices for sensing muscular contractions and for applying muscular stimulation, including: U.S. Pat. Nos. 6,091,977 to Tarjan et al., 6,104,960 to Duysens et al., 6,086,525 to Davey et al., 4,926,865 to Oman, 4,392,496 to Stanton, and 6,146,335 to Gozani, which are incorporated herein by reference.
U.S. Pat. No. 6,119,516 to Hock, which is incorporated herein by reference, describes a biofeedback system, optionally including a piezoelectric element, which measures the motions of joints in the body.
U.S. Pat. No. 5,069,680 to Grandjean, which is incorporated herein by reference, describes the use of a piezoelectric crystal as a muscle activity sensor.
U.S. Pat. Nos. 4,602,624 to Naples et al., and 5,505,201 to Grill, Jr., et al., which are incorporated herein by reference, disclose techniques for making implantable electrodes.
In an article entitled, “Gender comparisons of the mechanomyographic responses to maximal concentric and eccentric isokinetic muscle actions,” Medicine & Science in Sports & Exercise, 30(12), December, 1998, pp. 1697-1702, which is incorporated herein by reference, experiments are described in which a piezoelectric crystal contact sensor was placed over the vastus lateralis muscle to sense the mechanical activity thereof.